Method of introducing halogens into electric lamps

ABSTRACT

IN THE PROCESS OF INTRODUCING A HALOGEN INTO A LAMP IN THE FORM OF A HALOGENATED HYDROCARBON, THE FEED CONDUIT OR EXHAUST TUBE IS HEATED AT A LOCALIZED AREA TO A TEMPERATURE SUF-   FICIENTLY HIGH TO DECOMPOSE THE HYDDROCARBON AND PRECIPITATE THE CARBON THEREAT BEFORE IT ENTERS THE LAMP.

United States Patent Inventor Theo Berlinghoi Landershoien, Germany Appl. No- 812,629 Filed Apr. 2, 1969 Patented June 28, 1971 Assignee Patent-Treuhand-Gesellschait Fur elektrische Gluhlampen mbI-I 7 Priority Apr. 26, 1968 Germany METHOD OF INTRODUCING HALOGENS INTO ELECTRIC LAMPS 6 Claims, 2 Drawing Figs.

US. Cl 316/7,

Int. Cl I-I0lj 9/20 [50] Field ofSearch 316/3,7, 11, 24, 25

[56] References Cited UNITED STATES PATENTS 1,994,231 3/1935 Schroter 316/11X 2,208,113 7/1940 B0nney,Jr. et a1. 316/11 2,540,647 2/1951 Bienfait 316/7 Primary Examiner-John F. Campbell Assistant Examiner-Richard Bernard Lazarus Artorn'eys--Otto Tichy, Henry P. Truesdell, Frank L.

Neuhauser and Oscar B. Waddell ABSTRACT: In the process of introducing a halogen into a lamp in the form of a halogenated hydrocarbon, the feed conduit or exhaust tube is heated at a localized area to a temperature sufficiently high to decompose the hydrocarbon and precipitate the carbon thereat before it enters the lamp.

PATENTEU JUN28 ISYI METHOD OF TNTRODUCENG HALOGENS INTO ELECTRIC LAMPS METHOD OF INTRODUCING HALOGENS lNTO ELECTRIC LAMPS Electric incandescent lamps are known per se wherein the bulb filling of rare or inert gases comprises an addition of halogens. With the aid of said halogen additive, a cyclic process takes place in the interior of the lamp while in operation. During said cycle the tungsten particles vaporized off the filament and otherwise deposited on the bulb wall react with the halogen at the operating temperature of the lamp bulb to form gaseous tungsten halides which are conveyed back to the filament. The tungsten halides decompose at the hot filament to the free halogens and to tungsten which is deposited on the filament. Incandescent lamps with a halogen additive to the fill gas display throughout their lifetime virtually no blackening, that is, their light output remains approximately constant during their period of service.

it is difficult to add to the fill gas the required proportion of halogens for the cyclic process in elemental form. It has therefore already been proposed to add to the fill gas halogen-containing compounds which can be easily closed, and to liberate the halogens from said compounds only inside the lamp. Particularly suited for said purpose are compounds which supply the free halogens or hydrogen halides, respectively, by thermal decomposition on the hot filament. Compounds of this type are, for example, halogenated hydrocarbons such as dibromomethane and the like (French Patent l,439,777), as well as iodine compounds like CH Said substances have, even at room temperature, a considerable vapor pressure; they may be dosed, however, without difficulties in the desired proportion and be mixed with the fill gas.

In the course of manufacturing incandescent lamps with halogen additive in the fill gas, the fill gases are introduced into the lamp envelopes with the admixed halogenated hydrocarbon at the desired pressure. Subsequent to sealing the lamp by tipping off the exhaust tube, the halogenated hydrocarbon introduced together with the fill gases is decomposed upon initiation of filament operation. The halogenated hydrocarbon decomposes at the hot filament to elemental halogen, hydrogen and/or hydrogen halide; moreover, elemental carbon is precipitated. At least part of the carbon may be deposited in the course of this decomposition on the tungsten filament and form a carbide. The generation of tungsten carbide on and in the filament, however, is most objectionable because embrittlement of the filament is entailed. The carbon formed during dissociation may also deposit on the bulb wall and form there a light-absorbing precipitate. The present invention overcomes said most serious drawbacks. It also makes is possible to increase the amount of halogen without adding too much, if any, carbon at the same time.

According to the invention the novel method of manufacture of incandescent lamps with an addition of gaseous halogens to the fill gas introduced by thermal decomposition of a dosed quantity of a halogenated hydrocarbon such as dibromomethane added to the fill gas, consists in that the thermal decomposition of the halogenated hydrocarbon added to the fill gas is effected prior to introduction into the lamp envelope by localized heating ofa section of the feed conduit to the lamp to a temperature above the decomposition temperature of the halogenated hydrocarbon. Preferably, a suitable section of the feed conduit ahead of the tipping off spot of the lamp is heated in a localized area to from 800 to about l200 C. The exhaust tube attached to the lamp envelope is considered as part of the feed conduit and particularly suited for said purpose.

In the manufacture of incandescent lamps according to the invention, the lamp envelopes connected with the exhaust head of the filling device by means of the exhaust tube are prepared for the filling at first in conventional manner, i.e., the lamp envelopes with the already incorporated filament are degassed and exhausted for purification and, eventually, an

additional flushing with an inert gas may take place for further purification. Now, the filling of an inert gas with the halogen additive is introduced in the prepared lamp. For this purpose, the interior of the lamp envelope is connected by way of the exhaust tube and feed conduit with the storage tank which contains the prepared mixture of inert gas with an addition of halogenated hydrocarbons such as, for example, 0.3 percent of dibromomethane.

The mixture of fill gas and halogenated hydrocarbon flows through the feed conduit from the storage tank to the lamp envelope. According to the invention, the feed conduit is heated in a localized area to a temperature above the decomposition temperature of the dibromomethane, namely, to from 800 to about l200 C. In that area, the dibromomethane contained in the fill gas of the lamp decomposes by precipitation of carbon and formation of elemental bromine or hydrogen bromide. The resulting mixture flows into the lamp envelope and, subsequently, the lamp is tipped off.

in the case of hydrocarbons of iodine, for example, gaseous decomposition products other than iodine vapor may be reduced or removed by freezing the lamp envelope to condense the iodine, exhausting the envelope, and then filling it with the desired inert gas. The decomposition of the halogenated hydrocarbon takes place at a relatively elevated temperature. Said decomposition must therefore be effected in a place of the feed conduit which is resistant to the elevated temperature as well as to the resulting halogens or hydrogen halides, respectively. The exhaust tube attached to the lamp envelope by means of which the connection with the feed conduit of the exhaust and filling device is effected, is usually made of fused silica or a fused silica resembling high-melting point glass. It is resistant to the halogens or hydrogen halides, respectively, which are formed during decomposition, and also resistant to the applied temperature. Thus, the decomposition of the gaseous mixture flowing into the lamp envelope promoted by local heating of the exhaust tube is preferably ef fected between the exhaust head and the tipping off spot. By decomposition of the fill gas mixture in front of the lamp envelope, elemental carbon is prevented from getting into the interior of the lamp. The formation of tungsten carbide on the filament and also the precipitation of light-absorbing spots of carbon on the internal wall surface of the lamp is thus prevented.

In the accompanying drawing, FIGS. 1 and 2 are somewhat schematic elevations in which the method according to the invention is further illustrated.

The filament 2 is disposed in the lamp envelope 1 of, for example, fused silica and supported by support 3 which may be of the type shown and claimed in Pat. No. 3,173,051 to Berlinghof et al. Exhaust tube 4 of fixed silica is attached to the lamp envelope. It connects the interior of the lamp with the exhausting and filling device (not shown). After a conventional pretreatment serving for purification, the halogen-containing gas filling is introduced into the lamp. The prepared mixture of fill gas and halogenated hydrocarbon, for example, argon with 0.3 percent of dibromomethane, flows through exhaust tube 4 which is heated according to the invention by suitable heat sources such as, for example, gas burners 5, in area 6 to above 800 C. In this area, the dibromomethane admixed with the fill gas decomposes and carbon 7 is precipitated. The mixture now formed of fill gas and bromine or hydrogen bromide, respectively, passes on to the interior of the lamp. Subsequent to introduction of the filling, the finished lamp is tipped off at 8.

It is likewise possible to effect decomposition of the fill gas mixture with precipitation of the carbon according to the invention within the feed conduit in another place, as shown in FIG. 2. Moreover, an intermediate tank 9 may be provided in the feed conduit which first receives the mixture of fill gas and halogens or hydrogen halides, respectively, resulting subsequent to decomposition of the initial fill gas mixture at area 6. The purified and wholly exhausted lamp envelopes are then filled from said intermediate tank 9.

What I claim as new and desire to secure by Letters Patent of the United States is:

lclaim:

1. In the method of manufacture of incandescent lamps comprising an addition of gaseous halogens to the fill gas, introduced by thermal decomposition of a dosed quantity of a halogenated hydrocarbon added to the fill gas, the improvement wherein the thermal decomposition of the halogenated hydrocarbon added to the fill gas is effected prior to introduction into the lamp envelope by localized heating ofa section of the feed conduit to the lamp to a temperature above the decomposition temperature of the halogenated hydrocarbon to precipitate carbon thereat.

2. The method of manufacture of incandescent lamps as defined in claim 1 wherein a section of the feed conduit is heated in front of the tipping off spot of the lamp in a localized area to from 800 to about 1200 C.

3. The method of manufacture of incandescent lamps as defined in claim 1 wherein the exhaust tube is heated in front of the tipping off spot of the lamp in a localized area to from 800 to about 1200 C.

4. The method of manufacture of incandescent lamps as defined in claim ll wherein a mixture of fill gas and added halogenated hydrocarbon subsequent to its thermal decomposition first flows into an intermediate tank disposed in the feed conduit from which tank the exhausted lamp envelopes are filled.

5. The method of manufacture of incandescent lamps as defined in claim 1 wherein the halogenated hydrocarbon is a hydrocarbon compound of bromine.

6. The method of manufacture of incandescent lamps as defined in claim 1 wherein the halogenated hydrocarbon is a hydrocarbon compound of iodine. 

